Wind turbines are used to produce electrical energy using a renewable resource and without combusting a fossil fuel. Generally, a wind turbine converts kinetic energy from the wind into mechanical energy and then subsequently converts the mechanical energy into electrical power. A horizontal-axis wind turbine includes a tower, a nacelle located at the apex of the tower, and a rotor that is supported in the nacelle. The rotor is coupled either directly or indirectly with a generator, which is housed inside the nacelle. The rotor includes a central hub and a plurality of blades (e.g., three blades) mounted thereto and extending radially therefrom. The blades may rotate relative to the hub so as to pitch the blades into or out of the wind.
A typical modern wind turbine has many moving parts that facilitate converting the kinetic energy of the wind into electrical energy. As such, a wind turbine typically includes many bearings that provide relative movement between adjacent parts in a relatively efficient, low-friction manner. For example, in many wind turbines the wind turbine blades are rotatably mounted to the hub so that a pitch mechanism may be used to control the pitch of the blades (e.g., rotate the blades about their longitudinal axis) relative to the wind direction and thereby optimize the operation of the wind turbine.
Conventionally, such blade bearings are configured as roller element bearings characterized by having a structural element disposed between the two components that are moving relative to one another. For example, a conventional blade bearing may include an outer race mounted to the rotor hub, an inner race mounted to the wind turbine blade, and a plurality of ball bearings disposed between the two races for supporting the loads and providing generally low-friction, relative movement between the blade and hub. Roller element bearings fail for any number of reasons, but ultimately their life is limited by surface fatigue and wear. Such limited-life components require regular maintenance so as to avoid larger scale failure modes. The replacement parts and maintenance for such limited-life components increase the overall costs of operating a wind turbine.
While roller element bearings are adequate for their intended purpose, manufacturers continually strive to improve the design, operating costs, and functionality of wind turbines. More particularly, wind turbine and bearing manufacturers strive for improved or alternate designs that extend the operating life of bearings, including blade bearings.